Tandem mass spectrometry (MS/MS, MSn) employing a Fourier-transform mass spectrometer with electrospray ionization will be applied to large biomolecules. Key objectives will be to obtain MSn data with high mass accuracy (errors <1 ppm) and high resolution (unit resolution or higher) for molecules of molecular weight >10 kDa, possibly up to 150-200 kDa. Fourier and Hadamard transform capabilities will allow all such MS and MS/MS, respectively, data to be collected simultaneously over a broad mass range (m/z >200) on femtomole or subfemtomole sample quantities. Ion cell improvements contributing to these higher capabilities will include ion excitation methods, rf excitation field uniformly, and electrostatic field homogeneity. Improved computer hardware and software will more efficiently utilize this unusually high volume of data. Specific ion-molecule reactions will be applied to the MS/MS characterization of these large multiply-charged ions. Applications studied will include surveying unknown biological system constituents, detailed structural characterization of biomolecules (sequences, adducts, S-S bridge linkages), routine assays of recombinant proteins, and quantitation of enzyme-substrate and receptor- ligand affinities. Fundamental research on unimolecular ion dissociations will be extended to large multiply-charged positive and negative ions, including the kinetic redistribution of excitation energy. MS information will be sought indicative of three-dimensional structures of gaseous biomolecule ions and protein folding.